Process of preparing electrodes



Patented Nov. 17, 1925.

umreo STATES PATENT OFFICE.

FRITZ BAHR, OF BERLIN, GERMANY, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A

CORPORATION OF NEW YORK.

PROCESS OF PREPARING ELECTRODES.

No Drawing.

T 0 all who 11b it may ammo/n:

Be it known that I, Fnrrz Bruin, a citizen of the German Realm, residing at Berlin, Germany, have invented certain new and useful Improvements in Processes of Preparing Electrodes, of which the following is a specification;

My invention relates to electric lamps and to the process of preparing electrodes therefor.

It is well known that the arc in an arc lamp with electrodes of high fusing temperature, such as tungsten and the like, which electrodes are usually sealed in a bulb and surrounded by a gas, are difficult to start and easily break down with a small reduction in the normal operating current. This difficulty has been remedied by using cathodes having thorium or thorium salts. Such electrodes are obtained by a sintering process which unfavorably affects the thorium constituent or its effect.

I have found that an electrode of such material which has to be. used as a cathode may be prepared as follows: A metal, such as tungsten, which is to be used as a cathode, is coupled up in a circuit in connection with an anode which consists of or contains thorium or thorium oxide and a metal, and an are set up between the anode and the oathode in an inert gaseous atmosphere such as hydrogen. lVhen this is done, I find that the cathode elementbecomes coated with the material from the anode. This cathode element may thereafter be used as a cathode Application filed December 11, 1922. Serial No. 606,295.

fore the coating has been applied to the cathode, the arc can only be started by the use of a comparatively high voltage, but after the coating appears, the arc can be started at a much lower voltage. Furtheia more, when a cathode thus coated-isemployed, the arc is much steadier and may be maintained to within possibly of the normal operating current" strength .of the lamp. Therefore, electrodes produced by the process described and used in the manner described insure a stable are and one easily started.

What I claim as new and desire to secure by Letters Patent of the United States, is;-

1. The process of transferring material of high electron emissivity from one electrode of an arc to the other electrode of the are by establishing an are between the electrodes in a sealed envelope.

2. The process of first transferring material of high electron emissivity from one electrode of an arc to the other electrode of the arc by establishing an are between the electrodes, one of which electrodes is provided with such material ina sealed envelope and thereafter operating the arc with the current reversed.

3. The process of transferring a thorium material from one electrode to the other within the sealed envelope by establishing an are between the arc electrode whereby by reversing the current the arc may be established at a lower voltage than in the first instance, one of said electrodes being provided with such material.

In witness whereof, I have hereunto set my hand this 21st day of November, 1922.

FRITZ BAHR. 

